The members of the filovirus family, Ebola (EBOV) and Marburg (MARV) viruses, cause a severe hemorrhagic disease in infected humans and non-human primates with high fatality rates. Infected individuals who go on to succumb to EBOV exhibit disregulated immune responses which appears to result from several factors, including viral mediated impairment and disregulation of innate immune responses and subsequent failure to develop protective adaptive immunity. Studies of both human survivors and in animal models of EBOV disease suggest that a well-regulated cytokine response early in the course of the infection may be crucial to the outcome of the disease. Understanding the earliest events that occur in the interaction of the virus with cells of the host immune systems should shed light on the important determinants that influence the ability of a host to control the infection. The important early events are likely to center around monocytes, macrophages, and dendritic cells (DCs). These cells not only orchestrate innate and adaptive immune responses but are also the initial targets of viral infection. However, the available data on how these cells respond to EBOV infection is fragmentary and often contradictory. Therefore, developing a conceptual framework to understand how EBOV affects early innate responses remains challenging. This U01 proposal brings together the expertise to carefully dissect the early events of EBOV infection and pathogenesis in vitro and in vivo. The main objectives of this proposal are to: identify key events that lead to disregulated immunity in fatal Ebola disease, identify correlates of protection in survivors of EBOV infection and identify potential targets for therapeutic intervention both early in the host innate immune response, and later when uncontrolled inflammatory responses ensue. The aims are to 1) characterize the profiles of early cytokine and chemokine expression in EBOV infection, and compare how they differ to highly pathogenic less pathogenic EBOV; 2) determine if Toll-like receptors (TLRs) are activated by EBOV, and/or if EBOV infection individually or globally inhibits TLR activation in innate cells; 3) characterize the early cytokine responses in vivo, determine the role of TLRs and TLR signaling pathways on the pathogenesis of EBOV in vivo, and the role of alarmins in the cytokine storm that is a hall-mark of the late stages of EBOV infection; and 4) dissect the differences in early innate immune responses in a non-human primate model of EBOV disease upon infection by different EBOV species. The ultimate goal of this work is to identify new targets for therapeutic intervention into EBOV hemorrhagic disease. RELEVANCE (See instructions): The overall goals of the experiments outlined in the application are relevant to the NIAID's goals of understanding immune mechanisms of virus control, including how viruses and cells of the host innate immune system interact. The experiments are designed to identify new potential target for therapeutic interventions in hemorrhagic fever virus infections.